This invention relates to a reinforcing material. A conventional reinforcing structure is shown in FIGS. 1(A), 1(B), and 1(C). A reinforcing member 4 is made of a thermosetting resin augmented with a reinforcing material composed of glass fibers and non-woven fabric. The reinforcing member 4 is affixed to the inner surface of a door outer panel 2 (metallic plate-like member 2a) of a door 1. Thereafter the reinforcing member 4 is hardened by heating.
In FIG. 1, 5 is the door inner panel, 6 is the door window sash, 7 is the side window glass and 8 is the outside door handle.
In the case of such a reinforcing structure, unless the thickness thereof is considerable, the reinforcing effect will be minimal. Hence, the amount of the resin material required to suitably reinforce a large panel would noticeably increase production costs and weight. Also, it is difficult for the reinforcing member to perfectly conform to the shape of the panel to be reinforced, if the reinforcing member is molded and hardened prior to being bonded to the plate-like member.
Even if a reinforcing structure is formed by bonding a reinforcing member of unhardened resin to the panel and thermosetting the same, the thick resin layer will not conform to a curved feature in the panel with small radius of curvature.
In either case, secure adhesion of the reinforcing member and the panel is difficult to achieve.
With the above problems in mind, a reinforced panel for an automobile was proposed. As illustrated in FIGS. 2(A) and 2(B), a thermosetting resinous reinforcing member 11 is made of a tough epoxy resin, for example, augmented with a reinforcing material 10 such as glass fibers. The reinforcing member 11 is bonded directly onto the inner surface 2a of a metallic panel 2 serving as a door outer panel, or on a coating film 9 plated onto said inner surface in advance for rust proofing.
A reinforcing rib 13 is formed by sandwiching a light-weight, rigid member 12 between the inner surface of the panel 2 and the thermosetting-resinous reinforcing member 11. The light-weight member 12 is made of an expandable material, and is shown before expansion in FIG. 2(A) and after expansion in FIG. 2(B).
As shown in FIG. 3, a reinforcing strip 14 is used to form the reinforcing rib 13. The reinforcing strip is made by laminating a sheet of unhardened resin material 16, such as an unhardened epoxy resin, on a strip of an expandable material 15 which has not yet expanded. Particularly the expandable material 15 is preferably a material which will expand irreversibly in response to heating, such as foamable polyethylene or expandable epoxy. By expanding the reinforcing strip by heating the same, for example, during the coating-drying step of automobile assembly, a bead-like projection 1 is formed.
However, if the expandable material 15 is simply covered with a flat layer of the resin material 16, then a step will be formed as shown in FIG. 3A. That is, the contours of the expandable material 15 will not match the surface of the resin material 16. As a result, when the edges of the resin material 16 are bonded to the panel 2, a gap or gaps will be formed on either side of the expandable material 15 as shown in FIG. 3B. This will prevent perfect adhesion of the resin material 16 to the panel 2. In addition, if the expandable material 15 protrudes from the resin material 16, it will not be convenient to transport the reinforcing material in rolled form or stacked form.